This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Meibomian lipids are the major component of the outermost layer of the tear film, the film that protects the surface of the eye. They are composed of a wide variety of lipid species, the majority of which are long chain wax esters, cholesterol esters and fatty acids. Because it forms the interface with air, the physical and chemical properties of the lipid layer are believed to be influential in tear film stability. We are interested in exploring the structure of Meibomian lipids from individuals with stable tear films and patients with dry eye disease (unstable tear films). Studies of Meibomian lipid monolayers have shown the mechanical properties of these lipids to be quite responsive to temperature. We would like to link these results to changes in the crystalline structure from 25[unreadable]C through the melting transition, which will indicate the melt temperature of the lipids. In some forms of dry eye disease the composition of these lipids is different than asymptomatic individuals. If the melt temperature changes significantly compared to body temperature, the ability of the lipids to spread and the mechanical properties of the lipid layer may be modified in such a way that the tear film becomes unstable. The goal of this study is to understand the inherent crystalline structure of Meibum from ?normal? and dry eye subjects as a function of temperature using small angle x-ray scattering. We hope that such studies will contribute to an understanding of which properties promote stability in the tear film, how they change with disease, and how they can be restored for individuals suffering from dry eye.